Psoriasis is a common dermatosis of unknown cause. It is characterized as a chronic inflammatory condition of human skin. Psoriasis is estimated to affect about 3% of the population in industrialized countries (Baroni, A., et al., 2004. J. Cutan. Pathol. 31:35-42.), and is typically characterized by erythrosquamous cutaneous lesions associated with abnormal patterns of keratinocyte growth and differentiation (Lebwohl, M. 2003., Lancet 361:1197-1204). The classic symptoms of psoriasis are raised, red patches of skin topped with loose, silvery scales, usually on the knees or elbows.
There are several types of psoriasis. Symptoms for each type may vary in severity and appear in a wide array of combinations. In general, the major symptoms of psoriasis include: Bright red areas of raised patches (plaques) on the skin, often covered with loose, silvery scales. Plaques can occur anywhere, but commonly they occur on the knees, elbows, scalp, hands, feet, or lower back. Nearly 90% of people with psoriasis have plaque-type psoriasis.
Other manifestations of psoriasis include tiny areas of bleeding when skin scales are picked or scraped off (Auspitz's sign). Some individuals experience mild scaling to thick, crusted plaques on the scalp. Some patients experience itching, especially during sudden flare-ups or when the psoriasis patches are in body folds, such as under the breasts or the buttocks.
Nail disorders are common, especially in severe psoriasis and include the following symptoms: tiny pits in the nails (not found with fungal nail infections); yellowish discoloration of the toenails and possibly the fingernails; separation of the end of the nail from the nail bed; and a buildup of skin debris under the nails.
Other symptoms of psoriasis may include symmetrical plaques on the same areas on both sides of the body (for example, both knees or both elbows).
In certain instances patients experience flare-ups of many raindrop-shaped patches. Called guttate psoriasis, this condition often follows an infection with Group A Beta-hemolytic Streptococcus pyogenes (Group A strep; GAS) and is the second most common type of psoriasis. It affects less than 10% of those with psoriasis.
Finally, some psoriasis patients experience joint swelling, tenderness, and pain (psoriatic arthritis). These symptoms may occur in up to 39% of people with psoriasis.
Koebner's phenomenon can occur when a person with psoriasis has an injury (such as a cut, burn, or excess sun exposure) to an area of the skin that is not affected by psoriasis. Psoriasis patches then appear on the injured skin or any other part of the skin from several days to about 2 weeks after the injury.
Inflammatory aspects of the disease involve dermal angiogenesis, infiltration of activated T cells, and increased cytokine levels. One of these cytokines, IL-15, triggers inflammatory cell recruitment, angiogenesis, and production of other inflammatory cytokines, including IFN-□ TNF-□, and IL-17, which are all upregulated in psoriatic lesions. Although psoriasis has an unknown etiology, certain trigger factors, including physical trauma and GAS infections as described above, have been hypothesized to provoke clinical manifestations of psoriasis (Schon, M. P., and W. H. Boehncke. 2005. N. Engl. J. Med. 352:1899-1912). Fungal organisms, including Candida albicans (Waldman, A. et al., 2001. Mycoses; 44:77-81) and Malassezia furfur (Baroni, A., et al., 2004. J. Cutan. Pathol. 31:35-42.), have also been associated with the development of psoriatic skin lesions, and differences have been observed in the Malassezia species distributions in healthy subjects and patients with psoriasis (Gupta, A. K., et al., 2001. Med. Mycol. 39:243-251.; Hernandez Hernandez, F., et al., 2003. Rev. Iberoam. Micol. 20:141-144.; Prohic, A. 2003. Croat; 11:10-16.). Recent studies have also begun to characterize bacterial populations of human skin by using culture-independent molecular techniques (Dekio, I., et al., (2005) J. Med. Microbiol.; 54(12):1231-1238.
The human skin has been considered to harbor a complex microbial ecosystem (Fredricks, D N. (2001); J Investig Dermatol Symp Proc 6, 167-169), with transient, short-term resident and long-term resident biota, based on the consistency with which they are isolated. Staphylococcus, Micrococcus, Corynebacterium, Brevibacteria, Propionibacteria, and Acinetobacter species, among others, are regularly cultivated from normal skin. Staphylococcus aureus, Streptococcus pyogenes, (GAS) and Pseudomonas aeruginosa may be transient colonizers, especially in pathological conditions. Environmental factors, such as temperature, humidity, and light exposure, and host factors, including gender, genotype, immune status, and cosmetic use, all may affect microbial composition, population size, and community structure.
Knowledge of the human skin biota, chiefly through cultivation-based studies, is considerably limited in assessing compositions of complex microbial communities. In contrast, broad-range PCR primers targeted to highly conserved regions makes possible the amplification of small subunit rRNA genes (16S rDNA) sequences from all bacterial species (Zoetendal, E G, Vaughan, E E & de Vos, W M. (2006) Mol Microbiol 59, 1639-1650), and the extensive and rapidly growing 16S rDNA database facilitates identification of sequences to the species or genus level (Schloss, P D & Handelsman, J. (2004) Microbiol Mol Biol Rev 68, 686-691). Such techniques are increasingly used for identifying bacterial species in complex environmental niches (Smit, E, Leeflang, P, Gommans, S, van den, B J, van Mil, S & Wernars, K. (2001) Appl Environ Microbiol 67, 2284-2291), including the human mouth, esophagus, stomach, intestine, feces, and vagina, and for clinical diagnosis (Harris, K A & Hartley, J C. (2003) J Med Microbiol 52, 685-691; Saglani, S, Harris, K A, Wallis, C & Hartley, J C. (2005) Arch Dis Child 90, 70-73).
Although certain fungal associations and genetic and immunological features of skin conditions such as psoriasis have been examined, the role of bacterial microbiota in psoriasis has not been understood. Thus, there remains a need for methods for diagnosing, treating and preventing skin conditions such as psoriasis, particularly based on characterizing and altering bacterial microbiota to alleviate the condition. Until the present studies, little has been known about the species composition in cutaneous skin samples, and in particular there has been no comparison between bacterial species composition in normal skin and in psoriatic lesions.